The present invention relates to the interconnection of optical waveguides and, more particularly, to a technique for the coupling of optical signals to misaligned waveguides located on different wafers.
In high capacity optical networks, an essential device is the Nxc3x97N crossconnect switch. The function of this switch is to provide at each node full connectivity among several incoming fibers, each carrying several wavelength channels [1-6]. (Note in this specification, a reference to another document is designated by a number in brackets to identify its location in a list of references found in the Appendix) In my above identified related patent application, I described a technique for implementing an Nxc3x97N crossbar switch by including orthogonal sets of planar switches directly joined together without fiber connections. This technique can be used for the design of a Nxc3x97N switch using the classical crossbar arrangement shown in FIG. 1. The basic purpose of the Nxc3x97N crossbar switch arrangement is to form a total of N2 paths without waveguide crossings. In operation, a switch connection between N inputs and N outputs is realized by the arrangement by activating N particular paths, while blocking the remaining paths. The N2 paths are produced by two sets of planar switches, arranged in input and output block arrays that are directly jointed together, with a rotation of ninety degrees between the two blocks as shown in FIG. 1. Each of the N input switches is connected to all N output switches, and each of the N output switches is connected to all N input switches. The input and output planar arrays of N switches are all identical, and they can be realized without waveguide crossings in integrated form.
A difficulty, with the above arrangement, is that it requires over the junction plane precise alignment between the input and output input an output arrays.
In accordance with the present invention, I have solved the above-described difficulty by using adaptive imaging to minimize alignment errors in the active paths. The arrangement can also reduce crosstalk, since it can be designed to perform as a switching arrangement substantially reducing transmission in the crosstalk paths.
In one embodiment, an Nxc3x97N optical cross-connect is constructed using orthogonal abutting of arrays of planar switches. If N is not too large, the optimum construction involves only two stages of planar switches, each incorporating an adaptive imaging arrangement allowing the input and output switches to be directly joined together without need for precise alignment.
My adaptive imaging arrangement technique may, more generally, be used to align a first waveguide on a first wafer to a second waveguide on a second wafer. In general, misalignments occur both in the plane of the first wafer and in the orthogonal direction. Therefore efficient correction requires in general that the two wafers be approximately orthogonal to each other, and two adaptive imaging arrangement are required, one in each wafer. Thus, my adaptive imaging arrangement technique may be used to maximize coupling between waveguides located on different wafers or, more generally, between two arrays of waveguides located on two arrays of abutting wafers. The arrangement can also be designed to perform as a switching device, capable of maximizing transmission when it is traversed by an intended signal, and also capable of minimizing transmission when it is only traversed by a crosstalk path.
In accordance with my invention, I disclosed an apparatus for interconnection of two or more optical waveguides comprising a first planar wafer having a first optical imaging device for selectively focusing a signal on a first optical waveguide to a first focal point located along a predefined first focal interval of an edge of the first wafer; a second waveguide located on a second planar wafer that has an abutting edge forming an intersection junction with the edge of the first wafer, the second wafer includes an optical imaging device for selectively coupling a signal on a second optical waveguide to a focal point located along a predefined focal interval of the abutting edge of the second wafer, the focal intervals of the first and second wafers intersect each other; and
wherein the first and second optical imaging devices each operate in response to a control signal to align their respective focal points with the intersection junction and thereby maximize signal coupling from the first optical waveguide to the second optical waveguide.
According to another aspect of my invention, the optical waveguide interconnection apparatus may be arranged as an Nxc3x97N optical cross-connect apparatus comprising
a first plurality of first planar wafers, each first wafer including an input optical waveguide connected to a 1xc3x97N switch, each of the N output waveguides of the switch having an optical imaging device for selectively coupling a signal to a focal point located along a predefined interval of the abutting edge of the first wafer, thus forming a first array of disjoint intervals, each corresponding to a particular output waveguide of a particular first wafer;
a second plurality of second planar wafers, each second wafer including an Nxc3x971 switch connected to an output optical waveguide, each of the N input waveguides of the switch having an optical imaging device for selectively coupling the optical waveguide to an input focal point located along a predefined interval of the abutting edge of said second wafer; thus forming a second array of disjoint intervals, each corresponding to a particular input waveguide of a particular second wafer;
wherein the plurality of first and second wafers are essentially abutted orthogonal to each other to form a grid of intersection junctions therebetween and wherein each interval of the first array intersect a corresponding interval of the second array; and
wherein each pair of optical imaging devices producing a pair of intersecting intervals are responsive to a control signal to align their respective focal points to enable the coupling of an optical signal from a first optical imaging device to a second optical device of said pair.
According to another aspect of my invention, I disclose a method of operating an apparatus for interconnecting optical waveguides comprising the steps of
abutting an first edge of a first planar wafer to a second edge of a second planar wafer, the first wafer having a first optical imaging device for selectively coupling a signal to a first focal point located along a first predefined interval of the first abutting edge of the first wafer and the second planar wafer having a second optical imaging device for selectively coupling a signal to a second focal point located along a second predefined interval of the second abutting edge of the second wafer so as to overlap said first predefined interval of the first abutting edge of the first wafer; and
selectively operating at least one of the first and second optical imaging devices to enable the first focal point to align with the second focal point to enable the coupling of an optical signal between the first optical imaging device and the second optical imaging device.